Brush for dynamo-electric machines



Feb. 7, 1928. 1,658,677

M. R. HANNA BRUSH FOR DYNAMO ELECTRIC MACHI NES Filed Julyl8, 1927Inventor Max R. Hanna His Attorney Patented F cl). 7, 1928.

UNITED STATES PATENT OFFICE.

MAX R. HANNA, E ERIE, PENNSYLVANIA, ASSIGNOR TO GENERAL ELECTRIC COM-PANY, A CORPORATION OF NEW YORK.

BRUSH FOR DYNAMIC-ELECTRIC MACHINES.

Application filed July 18, 1927. Serial No. 206,478.

My invention relates to brushes for inc-electric machines.

Soft graphitic carbon brushes of low resistance are desirable for use indynamo-electrio machines when the current flow through the contact faceof the brushes is of high density. However, under some circumstances ithas not been feasible to employ these brushes for the reason that theysometimes wear away rapidly and must be replaced. For example, brushesof this character improve commutation in railway car motors undercertain operating conditions, but they have not been used because thecommutators of such motors arelikely to become pitted and roughened sothat the brushes would be worn away and the circuit to the motorinterrupted before the car could be returned to the shop for repair.

The object of my invention is to provide a brush having a soft tip whichwill be satisfactory where the density of current flowing through thecontact face of the brush is high, and having a hard portion arranged sothat in the event the current collecting device should become roughenedand the soft tip worn away that the hard portion of the brush will bebrought intocontactwith the current collecting device, which preventsthe brush being so worn as to interrupt the circuit to the machine inwhich it is used before the brushes are inspected in the usual course ofoperation.

My invention will be more fully set forth in thefollowing descriptionreferring to the accompanying drawing and the features of j noveltywhich characterize my invention will dynabe pointed out withparticularity in the b claims annexed to and this specification.

The single figure of the drawing illustrates a brush made in accordancewith my invention.

Referring to the drawing, my improved brush 10 comprises a softgraphitic carbon tip 10 and a hard carbon back 10". The soft material ofthe tip 10 is selected with a view of giving good commutation when themachine employing the brush is heavily forming a part of loaded. On theother hand the hard back i0 is made of a material hard enough to revsist wear and tends to smooth the current collecting device. Goodelectrical conductivity of the brush is obtained preferably by mouldingthe soft tip- 10 and the hard back 10' integrally in the process ofmaking the brush, which is carried out in the usual manner. However, thesoft tip and the hard back of the brush may be cemented together orjoinedtogether mechanically in any suitable manner, as for example, bythe use of any convenient metallic reinforcement. The brush is supportedin operative relation to the surface 11 of the current collec'tingdevice by a brush holder 12, of any suitable. form, having a spring 13which exerts the desired brush pressure on the current collectingdevice.

During operation of a machine employing a brush of this form the softcarbon tip 10 insures good commutation when heavy current flows throughthe contact face of the brush. Moreover, in the event the currentcollecting device should become roughened, although the soft tip away,yet the hard back l0 would be brought into contact with'the surface ofthe current collecting device. the brush resists being worn away by theroughened current collecting device and smooths the face of thecommutator, so that the circuit to the machine is not interrupted beforethe brushes are inspected and replaced.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is 1. A brush for a dynamo-electric machine having a tipof softmaterial adapted to ear on a current collecting device, and a portion ofhard material adjacent said tip adapted to form a contact face of thebrush when the soft material is worn away.

2. A brush for a dynamo-electric machine having a tip of soft graphiticcarbon, and a back of hard carbon united with said tip adapted to forma. contact face of the brush a" when said tip is worn away.

In witness whereof, I have hereun o sci, my hand this 14 day of July,1927.

MAX R. HANNA.

10 would be worn The back 10 of.

